1. Field
The disclosed embodiments concern a by-pass device of an electrical component, such as a module by-pass device, and more particularly a thermally activated by-pass device using a control current. It finds application more particularly in the isolation and short-circuiting of a battery element, which has become defective.
2. Brief Description of Related Developments
Protection against defective batteries has been the subject of numerous studies, in particular of difficult to access batteries, such as those on board space missiles.
In fact, when a battery element becomes defective, it is imperative to isolate it so that it shall not impair the functioning of sound battery elements, which may continue to work and to supply potential to the circuit, which the battery has to supply.
Generally speaking, by-pass devices also called battery by-passes, consist of an actuator, a trigger and a reversing switch located in a housing, each of these three components possessing its own function. Thus, the actuator is a mechanical device, which has to be able to provide the transposition between two positions of a control device called a shaft or a plunger. The trigger is a mechanical device comprising a fusible material, which when subjected to an electric control current producing a rise in temperature will melt or break in order to set free the actuator. The reversing switch is a device, which provides in each of its two positions electrical continuity between two of the three terminals carried by the housing and connected to the battery element circuit terminals.
At one of its ends, the shaft generally speaking comprises a flange, which serves as a stop to a spring located in the space provided between the shaft and the internal wall of the housing. This space comprises a circular shoulder cut the internal surface of the housing in such a way as to trap the spring between the shaft collar and the circular shoulder. The spring is thus kept in compression, whilst the shaft is held in sheathed position by the trigger, that is to say, when the shaft holds the reversing switch in its normal position of functioning and when electrical continuity between the two first terminals is provided. In the event of the dysfunction of a battery element, the trigger is actuated and thereby sets free the shaft. The latter is then transposed from its sheathed position to the freed position under the pressure of the spring. This position freed by the trigger makes it possible for the shaft to bring the reversing switch into a position of isolation of the failed battery element by providing electrical continuity between a first and a second terminal.
Triggers which use a fusible material, which melts or breaks on a rise in temperature of the material by the passage of an electric current, are well known.
This principle is described in U.S. Pat. No. 3,388,933, which deals with a trigger comprising a fusible element, which keeps half-shells able to be separated for the purpose of the maintenance and the setting free of a voluminous object fixing hoop.
An application of this principle is, in particular, disclosed by U.S. Pat. No. 3,924,688, which describes the setting free of an actuator shaft kept in contact by two locked half-shells by means of a wire coil under strain, whose slackening is controlled by the melting of a fusible element. The slackening of the coil makes possible the separation of the two half-shells and hence the setting free of the shaft.
An improvement to this principle is disclosed in U.S. Pat. No. 5,471,888, which describes an embodiment comprising two half-shells and an insulator on which the fusible element is placed.
The technology of actuators making possible the separation of an element of a battery when the latter exhibits an anomaly, by a physical separation of the two parts of an assembly, thanks to the melting of an element reacting to an electrical threshold, is likewise well known.
U.S. Pat. No. 5,362,576 concerns a conducting plunger placed between two terminals constituting the ends of an insulating cylinder. An output terminal is connected to the battery element. When it is functioning normally, the plunger is kept in electrical contact with the terminal through a fusible element. The current then passes between the terminals through the plunger, which also comprises peripheral contacts in the form of metal sleeves. When an electric threshold is exceeded, corresponding to an increase of the internal resistance of the battery element, the thermal element weakens, melts and breaks. The plunger is then propelled through the relaxing of the strain of the spring and after having broken the electrical continuity between the first terminals, provides a by-pass connection by connecting the first and second terminal.
U.S. Pat. No. 5,438,173 deals with a battery by-pass device comprising a mobile mounting consisting of a base, a compression spring, an element comprising erasable arms, which hold in place a plunger. The said plunger is equipped with a freeing means which comes into play in the case of a failure via the erasure of the arms, thus setting free the mobile mounting and making it possible to establish an electrical by-pass circuit.
U.S. Pat. No. 6,249,063 discloses a conducting half-shaft, carrying toroidal contacts, mechanically connected to an insulating half-shaft providing electrical continuity between the terminals, the plunger connected mechanically to the insulating half-shaft being held by two half-shells, themselves held in contact by a wire coil under strain, the said strain being released when a fusible element on its electrical threshold is destroyed. More particularly this document describes a modular by-pass device of an electrical component comprising a housing possessing a movable means of sealing and equipped with conducting terminals, one of whose ends is connected to one of the terminals of the electrical component circuit, the other end being fastened to the wall of the housing projecting into the interior of the housing and constituting a contact post, an actuator providing transposition between two positions of a control device consisting of a plunger shaft and comprising a spring arranged in the space formed between the plunger shaft and the internal wall of the housing, a trigger comprising a retention device of the plunger shaft held in place by a fusible material, a reversing switch comprising a contact zone providing electrical continuity between two contact posts of the terminals carried by the housing.
All the embodiments described in the prior art use a relatively large number of parts, which may become separated when used in demanding environments, which are costly to assemble and which cannot be used in all models required by customers. Moreover, the said large number of parts does not make possible easy on-site assembly, maintenance or repair of the devices.
There is accordingly a need to provide a modular by-pass device of an electrical component offering a high degree of flexibility in use, for the adaptation, the introduction and the replacement of different components.
Such a device must be modular and must moreover make possible absolute safety, in order to avoid during the assembly and fitting in workshops, any danger of untimely triggering. Lastly, in the event of
untimely triggering, the device must make possible the repositioning of components without complete dismantling.